Conventional analog telephony (also known as “Plain Old Telephone Service”, or “POTS”) is based on a central office (CO) or private branch exchange (PBX) connected to telephone sets using a wire pair known as a ‘subscriber loop’. In most cases, the telephone set side of the wiring in a building is terminated using telephone outlets, into which the telephone sets are connected. The PBX/CO provides a low-voltage (usually around 48VDC) low-power direct current in order to detect a telephone off-hook/on-hook condition of a telephone connected to that line. In a conventional analog telephone, lifting the handset off the cradle (off-hook condition), closes a switch that places a resistive load across the line, causing a direct current to flow in the subscriber loop. This current is detected at the PBX/CO to signal the telephone off-hook condition, and also for legacy ‘Pulse Dialing’ switching systems. Although originally intended only for detecting the telephone off-hook condition and Pulse Dialing, this DC power has also been widely used to provide low-voltage electrical power for other purposes, such as electronic circuitry used in telephonic devices and related apparatus associated with use of the telephone lines for communication and data transmission.
For purposes of this invention, any facility providing a local telephone line to one or more telephones is considered to be functionally equivalent to a Private Branch Exchange (PBX), a Central Office (CO), or similar system, and is herein denoted by the term “PBX/CO”.
FIG. 1 is a schematic diagram illustrating a basic in-house PBX/CO-to-telephone connection arrangement 10. A PBX/CO 11 has a 2-wire telephone line local or subscriber loop constituted by wiring 14 to which telephone sets 13a and 13b are connected via respective 2-wire connecting lines. A “telephone set” includes, but is not limited to, telephones, fax machines, dial up modems, and any other telephonic devices. In most cases, the telephone sets connect to the telephone wiring by means of telephone outlets 12a and 12b, respectively.
While wiring 14 in a premises is normally based on a serial or “daisy-chained” topology, wherein the wiring is connected from one outlet to the next in a linear manner; other topologies such as star, tree, or any arbitrary topology may also be used. Regardless of the topology, however, the telephone wiring system within a residence always uses wired media: two or four copper wires terminating in one or more outlets that provide direct access to these wires for connecting to telephone sets.
The term “telephone outlet” herein denotes an electro-mechanical device that facilitates easy, rapid connection and disconnection of external devices to and from telephone wiring installed within a building. A telephone outlet commonly has a fixed connection to the wiring, and permits the easy connection of external devices as desired, commonly by means of an integrated connector in a faceplate. The outlet is normally mechanically attached to, or mounted in, a wall. A “telephone outlet”, as used herein, can also be a device composed of a part that has a fixed connection to the wiring and is mechanically attached to, or mounted in, a wall, and a part that is removably mechanically attached and electrically connected to the first-mentioned part, i.e. a device in which the first part is which is a jack or connector used for both electrical connection and mechanical attachment. The term “wall” herein denotes any interior or exterior surface of a building, including, but not limited to, ceilings and floors, in addition to vertical walls.
It would be desirable to have the possibility of carrying power over active telephone lines in addition to the telephone signals. This would, among other things, obviate the need to install additional cabling in installations wherein telephone wiring already exists. For example, power carried over a telephone line may be used to power repeaters, as well as any other mediation devices throughout the telephone wiring, multi-features telephone sets, and other telephony related and non-telephony devices. The powering is usually required when the connected telephones are off-hook and on-hook.
U.S. Pat. No. 6,216,160 to Dichter and US Patent Application Publication 2002/0003873 to Rabenko et al. disclose carrying AC power over active telephone wiring, using frequency domain multiplexing (FDM) in order to avoid interference with the telephony signals, as well as other signals carried over the telephone wiring. This approach to supplying power has drawbacks due to the radiation limitation imposed on non-shielded telephone wiring, for example by the FCC. Furthermore, such implementation requires very complex and expensive filtering circuits.
U.S. Pat. No. 6,157,716 to Ortel discloses a technique for carrying DC power over active telephone lines. Based on a diode and on the impedances exhibited in the various on- and off-hook states, DC current can be imposed and extracted using the telephone lines. Using DC powering reduces the radiation and filtering problems associated with the AC powering. However, the technique disclosed by Ortel allows only for a very limited amount of power to be carried over the telephone wiring.
A general prior art system 20 is shown in FIG. 2 and differs from system 10 by including a Power Supply Coupler (PSC) 21, which is supplied with power from power supply 22 and couples that power onto active telephone wiring 14. Power supply 22 is powered from the utility AC mains via a standard plug 25. A load Coupler 23 extracts the power from the telephone line and feeds a load 24. In such a system, power supply 22 feeds load 24 using the active telephone wiring 14, with the goal of minimum interference to the telephone signals carried simultaneously over the wiring 14.
It would be highly advantageous to have a system for providing increased amounts of DC power to power remote devices via active telephone lines, such as those served by a PBX/CO in a building or within an office. This goal is met by the present invention.